Current-Voltage Characteristics of the Plasma Focus: A Deeper Look

Sor Heoh SAW, Sing LEE

Abstract


A capacitor bank discharges a current which is a sinusoidal function, lightly damped by unavoidable circuit resistance. When powering a plasma focus, the current waveform is further damped by the axial motion typically during the rising part of the current. The radial phase, with severe rate of change of inductance due to a rapidly collapsing current sheet to a small radius, is so severely damped over a short period near the current peak that the waveform goes into the sharp dip. This produces the well-known signature current dip of the properly-operated plasma focus. Corresponding to the inductively-caused current dip is a sharp voltage spike which typically rises to a peak value in excess of the voltage to which the capacitor is charged. These features are adequately described by circuit equations coupled to appropriate equations of motion. The loading effect of different gases due to differences in mass, differences in compressibility and differences in radiation also produces differences in the current waveforms particularly in the current dips and voltage spikes. These differences could be subtle or dramatic, as are demonstrated in this paper.

Keywords


Dense plasma focus, current-voltage characteristics, high density plasma, compressibility, radiation collapse

Full Text:

PDF

References


SP Thong and S Lee. A Simplified method of switching a 2 mega-ampere capacitor bank using a voltage division technique. Malaysian J. Sci. 1973; 2, 157-69.

S Lee. Plasma focus radiative model: Review of the Lee model code. J. Fusion Energ. 2014; 33, 319-35.

S Lee. Radiative Dense Plasma Focus Computation Package: RADPF. Available at: http://www.plasmafocus.net/IPFS/modelpackage/File1RADPF.htm, accessed October 2017.

S Lee and SH Saw. Course on plasma focus numerical experiments manual. In: Proceeding of the Joint ICTP-IAEA Workshop on Dense Magnetized Plasmas and Plasma Diagnostics. Trieste, Italy, 2010.

S Lee, SH Saw and J Ali. Numerical experiments on radiative cooling and collapse in plasma focus operated in Krypton. J. Fusion Energ. 2012; 32, 42-9.

M Akel and S Lee. Radiative collapse in plasma focus operated with heavy noble gases. J. Fusion Energ. 2013; 32, 111-6.

R Pease. Equilibrium characteristics of a pinched gas discharge cooled by Bremsstrahlung radiation. Proc. Phys. Soc.1957; 70, 11.

SI Braginskii. The behavior of a completely ionized plasma in a strong magnetic field. Zh. Eksp. Teor. Fiz. 1957; 33, 645.

K Koshelev and N Pereira. Plasma points and radiative collapse in vacuum sparks. J. Appl. Phys. 1991; 69, 21-44.

S Lee, SH Saw, M Akel, HJ Kunze, P Kubes and M Paduch. Conditions for radiative cooling and collapse in plasma focus illustrated with numerical experiments on the PF1000. IEEE Trans. Plasma Sci. 2016; 44, 165-73.

S Lee. Radius ratio of argon pinches. Aust. J. Phys. 1983; 3, 891-5.

SH Saw and S Lee. Measurement of radiative collapse in 2.2 kJ PF: Achieving high energy density (HED) conditions in a small plasma focus. J. Fusion Energ. 2016; 35, 702-8.


Refbacks

  • There are currently no refbacks.




http://wjst.wu.ac.th/public/site/images/admin/image012_400

Online ISSN: 2228-835X

http://wjst.wu.ac.th

Last updated: 13 February 2019